This invention relates to a control system and operator interface for a laser, and particularly for an electric discharge laser used in an industrial application.
Lasers for industrial applications, such as KrF or ArF electric discharge lasers for microlithography (see U.S. Pat. No. 4,959,840, issued Sep. 25, 1990 to Akins, et al.), typically incorporate a laser controller, resident at the laser. Input and output interfaces to the laser controller are typically provided in two ways: (i) through an operator actuated hand held terminal, and/or (ii) through a workstation controller that acts as a master controller, with the resident laser controller acting as its slave. The workstation controller primarily controls and synchronizes workstation subsystems, such as workpiece positioning and orientation and other process functions relating to the specific industrial application. The interface specifications between the laser controller and the workstation controller may vary greatly, depending on the application. For example in microlithography, subsystems include the laser, illumination system, projection system, and scanner.
A primary function of the hand held terminal is to operate the laser independently of the workstation and application. The hand held terminal typically permits complete operation of the laser by a human operator and acts as a primary means of communication between the laser and the operator. For example, all laser status conditions (e.g., operational state, operational errors, etc.) are communicated from the resident laser controller to the operator, usually by visual display, through the hand held terminal. Likewise, the operator can control various functions of the laser, e.g., changing the operating state, by depressing a prescribed key in the hand held terminal. The keystroke is interpreted by the hand held terminal, translated to an appropriate electrical command, and serially communicated to the resident laser controller.
Control of the laser by the operator is greatly enhanced by the ability to sequence various keystrokes. For example, the operator can sequentially change the operating state of the laser, perform a gas refill, again change the operating state of the laser, and run the laser by a prescribed sequence of keystrokes. Conversely, the laser controller keeps the operator informed of the status of the laser by displaying relevant information at the hand held terminal.
Frequently, a laser operator is required to perform repetitive operations with a laser. For example, when a new laser chamber is installed, the operator performs a sequence of gas refills, each followed by operation of the laser under different prescribed conditions. The operator typically repeats these operations until the laser meets certain performance criteria. Similarly, an operator typically performs a weekly diagnostic check, filling the laser with a prescribed gas composition, operating the laser under different prescribed conditions, and check the magnitudes of prescribed laser operating parameters. Typically these magnitudes are then manually recorded by the operator in a log sheet. In some cases, when a number of operations are sequenced, an operator may omit an operation or perform an operation out of sequence, thereby obtaining erroneous results. Similarly, an operator may inadvertently record data erroneously in a manual log sheet. In either case, the consistency and accuracy of data is suspect, and the results can have adverse consequences for the performance of the laser and/or of the application.
It is therefore desirable in the art to provide a method and apparatus that minimize an operator""s repetitious tasks, reduces the probability of operator error, and enhances the reliability of recording laser operating status data.
A laser controller interconnected with an electric discharge laser communicates with a remote computer incorporating a display screen programmably emulating a conventional input device (e.g., standard computer keyboard, keypad, touchpad). The display screen has a plurality of imaged virtual keys each programmably emulating a physical key of the conventional input device, and at least one of the virtual keys is programmably configured to emulate a predefined sequence of keystrokes. The remote computer is interconnected to the laser controller with an electrically conductive cable, or alternatively through a fiberoptic link or over a wireless communication channel. The virtual keys can include a function key and/or a xe2x80x9cLASER OFFxe2x80x9d key.
A keystroke is applied by manually pressing the position of a corresponding virtual key on a touch sensitive screen, or alternatively by actuating a pointing device. In some embodiments of the present invention a prescribed sequence is automated, whereas in some embodiments a sequence is conditioned on a measured value or on operator response to a prompt. In a preferred embodiment, a keystroke is applied at a remote computer, serially communicating signals in response to the keystroke, to effect an action at an electric discharge laser. Actions can include measuring, recording, and/or changing values of laser parameters, or sequences including any or all of these functions. A prescribed sequence is typically defined according to a programmably created script that links a desired sequence of operations to a preselected keystroke.
The electric discharge laser can be a KrF or ArF excimer laser, or a F2 molecular laser, which can provide a radiation exposure source for microlithography.